Wireless energy transfer is the transmission of electrical energy from a power source to an electrical load without the use of interconnecting conductors. Wireless transmission can be useful when one has many electrical loads to charge, where the use of interconnecting wires may be inconvenient.
Wireless charging pads make use of electrodynamic induction, and are a common method of successfully transferring energy without the use of wires. When an electrical device that needs to be charged, such as a cell phone, needs to be charged, it is set on top of the pad and energy transferred from the pad will charge the cell phone battery. Wireless energy transfer is limited by the ability of the cell phone battery being capable of receiving and using the transmitted power.
Some wireless power transfer systems may be required to operate from a variety of input power sources. For example, the mobile phone wireless charging pad can be normally powered from the wall adapter with the adequate power rating. At the same time, it is highly desirable that the same part operates when powered from a USB port or power sources that harvest electrical energy from renewable energy sources.
A USB port normally provides substantially lower power output (2.5 W) than a wall adapter (6.5 W), while both have the same output voltage level. In current wireless power transfer systems, this can present a problem as the wireless charging pad has no means to communicate to the remote part of the wireless power transfer system.
The remote part of the wireless power transfer system will attempt to draw a nominal load current despite the limited input. This will effectively render the wireless power transfer system inoperable.
What is needed is a system and method for distinguishing between power capabilities of input sources and a means of communicating the identified power capability to the secondary side of the wireless power transfer system.